In many memory devices, including random access memory (RAM) devices, data is typically accessed by supplying an address to an array of memory cells and then reading data from the memory cells that reside at the supplied address. However, in content addressable memory (CAM) devices, data within an array of memory cells is generally not accessed by supplying an address, but rather by initially applying data (e.g., a search word) to the array and then performing a search operation to identify the location of one or more entries within the array that contain data equivalent to the applied data. In this manner, data is accessed according to its content rather than its address. Upon completion of the search operation, the identified location containing the equivalent data is typically encoded to provide an address at which the matching entry is located. If multiple locations with matching entries are identified in response to the search operation, then priority encoding operations can be performed to identify an address of a best or highest priority matching entry.
A ternary content addressable memory (TCAM) device is a specific type of CAM device for performing the above noted functionality. A TCAM device includes an array of ternary memory cells. As opposed to typical memory cells that store only one bit of digital information, each ternary memory cell stores two bits of digital information that represent either logic zero, logic one, or logic don't care (i.e., a wildcard value that can represent either logic zero or logic one). The bits stored within a row of ternary memory cells in a TCAM device often constitute a data word. During search operations, a search word is applied to appropriate input terminals of the TCAM and then compared with the data words stored in each row of the array of ternary memory cells. For each stored data word that matches the search word, an associated match line signal is asserted to indicate a match condition.
The embodiments of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.